Causes of Acute Diarrhea
Acute diarrhea is most commonly caused by viral gastroenteritis (particularly norovirus), followed by bacterial pathogens including Salmonella, Campylobacter, Shigella, Shiga toxin-producing E. coli (STEC), and Clostridioides difficile, with parasitic causes being less common in developed countries 1, 2.
Infectious Causes
Viral Pathogens (Most Common)
- Norovirus is the leading viral cause of acute diarrhea in adults 2
- Other viral agents cause self-limited disease, typically presenting as noninflammatory diarrhea 1
- These pathogens disrupt enterocyte absorptive/secretory processes without causing acute inflammation or mucosal destruction 3
Bacterial Pathogens
The bacterial causes can be categorized by mechanism:
Noninflammatory (Enterotoxin-Producing):
- Enterotoxigenic E. coli (ETEC)
- Vibrio cholerae
- These organisms produce enterotoxins that disrupt fluid balance without invading tissue 3
Inflammatory/Invasive Pathogens: The 2017 IDSA guidelines specifically identify the most clinically important bacterial causes in North America as 4:
- Salmonella (causes most hospitalizations and deaths in the U.S.) 2
- Campylobacter
- Shigella
- STEC (including O157:H7)
- Clostridioides difficile (incidence has doubled since 2001, increasingly seen in community-acquired cases with minimal antibiotic exposure) 4
These pathogens either produce cytotoxins or directly invade intestinal mucosa, triggering inflammatory mediator release and cytokine activation 3.
Parasitic Causes
- Less common in developed countries with adequate sanitation
- Include Giardia lamblia and Entamoeba histolytica 5
Noninfectious Causes
While the guidelines focus primarily on infectious etiologies, noninfectious causes exist for both inflammatory and noninflammatory diarrhea 1. These include:
- Medication-related diarrhea
- Food intolerances
- Inflammatory bowel disease flares
Clinical Differentiation
Key distinguishing features that suggest specific causes:
- Fever + bloody diarrhea → Consider invasive bacterial pathogens (Salmonella, Shigella, Campylobacter) 4
- Bloody diarrhea WITHOUT fever → Strongly consider STEC infection 4
- Recent hospitalization or antibiotic use → C. difficile (though community-acquired cases are increasing) 4
- Travel history to endemic areas → Enteric fever (Salmonella Typhi/Paratyphi) 4
- Foodborne or waterborne exposure → Various bacterial pathogens 1
Important Clinical Caveat
Most acute diarrhea episodes in countries with adequate food and water sanitation are uncomplicated, self-limited, and viral in etiology 1. The presence of inflammatory features (fever, bloody/mucoid stools) or specific risk factors (immunocompromise, recent hospitalization, severe dehydration) should trigger consideration of bacterial causes and potential need for diagnostic evaluation 4, 1.
The mechanism-based classification (noninflammatory vs. inflammatory) is more clinically useful than simply listing pathogens, as it guides both diagnostic approach and management decisions 3.